A commonly used piezoelectric material is an ABO3-type perovskite metal oxide such as lead titanate zirconate (hereinafter, referred to as “PZT”). However, it is considered that PZT, which contains lead as an A-site element, may cause environmental problems. Therefore, a piezoelectric material with a lead-free perovskite-type metal oxide has been desired.
Barium titanate is known as a piezoelectric material with a lead-free perovskite-type metal oxide. Patent Literature 1 discloses barium titanate prepared by a resistance heating/two-step sintering technique. The patent literature describes that a ceramic with excellent piezoelectric property can be obtained when nano-sized barium titanate powder is sintered by the two-step sintering technique. However, the barium titanate has a problem that it is not suitable for device operation at high temperature because its Curie temperature is low at 125° C.
In addition, Non-Patent Literature 1 discloses a solid solution of barium titanate and bismuth ferrite as an attempt to increase the Curie temperature of barium titanate. However, as the solid solution amount of the bismuth ferrite increases, the Curie temperature increases while piezoelectric performance is conspicuously decreased.
In other words, it is difficult to achieve both high piezoelectric performance and high Curie temperature in a piezoelectric material of the lead-free perovskite-type metal oxide.